1. Field of the Invention
The present invention relates to a high efficiecy power amplifier circuit with a wide dynamic range, a control method for the power amplifier circuit, and a portable terminal apparatus for mobile communication.
2. Description of the Related Art
For example, CDMA portable terminals are seldom operated at maximum power, but are often operated at 10 to 20 dB lower power. Thus, in order to extend battery life of terminals, it is important to reduce power consumption during such low power operation.
FIG. 11 shows a conventional power amplifier which can reduce power consumption during such low power operation.
In FIG. 11, the power amplifier consists of an input terminal 1101, output terminal 1102, matching circuit 1103, transistor 1104, matching circuit 1105, bias circuit 1106, bias circuit 1107, step-down DC/DC converter 1108, and control means 1109.
The conventional power amplifier impedance-matches an input signal entered from the input terminal 1101 using the matching circuit 1103, amplifies the signal using the transistor 1104, impedance-matches the signal using the matching circuit 1105, and outputs the signal from the output terminal 1102.
The step-down DC/DC converter 1108 adjusts the supply voltage fed from a power supply terminal 1111 by lowering an output voltage to be delivered to the bias circuit 1107, under the control of the control means 1109.
Specifically, the conventional power amplifier achieves high efficiency with a wide dynamic range by using the step-down DC/DC converter 1108, which sets the collector or drain voltage of the transistor 1104 to a value equal to or slightly lower than the supply voltage from the voltage supply terminal 1111 when the output power from the output terminal 1102 is high and sets the collector or drain voltage of the transistor 1104 to a value much lower than the supply voltage from the voltage supply terminal 1111 when the output power from the output terminal 1102 is low. Thus, conventionally, the collector or drain voltage of the transistor has never been used at a level higher than the supply voltage.
Besides, with the power amplifier used for CDMA or other portable terminals, an isolator is placed between the power amplifier and an antenna to reduce load variations in the power amplifier.
FIG. 13 shows such a conventional power amplifier 1302.
During reception, an antenna switch (or antenna duplexer) 1304 outputs signals received by an antenna 1306 to an output terminal 1305 for received signals.
During transmission, the power amplifier 1302 amplifies transmitted signals entered from an input terminal 1301 for transmitted signals and outputs them to an isolator 1303, which in turn sends the output of the power amplifier 1302 to the antenna switch (or antenna duplexer) 1304, which then routes the output of the isolator 1303 to the antenna 1306.
Antenna 1306 load will change during transmission, for example, due to causes such as a human body approaching the antenna 1306. However, even if the antenna load changes in this way, the isolator 1303 placed between the power amplifier 1302 and antenna switch (or antenna duplexer) 1304 keeps the load on the output side of the power amplifier 1302 virtually almost constant.
FIG. 12B shows characteristics of the step-down DC/DC converter 1108 used in the power amplifier shown in FIG. 11. FIG. 12A shows the step-down DC/DC converter 1108, where reference character Vin denotes an input voltage fed to the step-down DC/DC converter 1108 from a power supply connected to the power supply terminal 1111 while reference character Vout denotes an output voltage produced by the step-down DC/DC converter 1108.
Specifically, in FIG. 12B, on the condition that the input voltage Vin is constant, the horizontal axis represents the output voltage Vout and the vertical axis represents efficiency (%) of the step-down DC/DC converter 1108. The efficiency here is the percent ratio of output power Pout to input power Pin when the input voltage Vin is applied to the power supply terminal 1111 and the output voltage Vout is produced. In short, the efficiency is given by Pout/Pinxc3x97100.
It can be seen from FIG. 12B that the efficiency lowers with decreases in the output voltage Vout of the step-down DC/DC converter 1108.
During the operation of the power amplifier shown in FIG. 11, actually the output power from the output terminal 1102 is relatively low in most cases. When the output power is low, so is the output voltage of the step-down DC/DC converter 1108. Therefore, as can be seen from FIG. 12B, when the power amplifier produces low output power, the voltage conversion ratio of the step-down DC/DC converter 1108 is high. In such cases, the conversion efficiency of the step-down DC/DC converter 1108 lowers. Since the conversion efficiency of the step-down DC/DC converter 1108 lowers under low power conditions in which the power amplifier is used frequently, there is not much reduction in power consumption.
That is, a problem with the conventional power amplifier is that its power consumption cannot be reduced due to the lowered conversion efficiency of the step-down DC/DC converter.
On the other hand, the isolator 1303 placed between the power amplifier 1302 and antenna switch (or antenna duplexer) 1304, described with reference to FIG. 13, poses a problem of increased circuit scale.
Also, the isolator 1303 causes a power loss of approximately 0.2 to 0.8 dB, for example. Thus, although load variations of the power amplifier 1302 can be reduced, the output power of the power amplifier 1302 must be increased to make up for the power loss caused by the isolator 1303. This results in increased power consumption.
That is, a problem with conventional power amplifier is that the isolator causes power loss, which when compensated for, results in increased power consumption.
In view of the problems with the conventional power amplifier described above, an object of the present invention is to provide a power amplifier circuit with a smaller circuit scale and with good characteristics over a wide range of load impedance, a control method for the power amplifier circuit, and a portable terminal apparatus using the power amplifier circuit. Another object of the present invention is to provide a highly efficient power amplifier circuit with a wide dynamic range, a control method for the power amplifier circuit, and a portable terminal apparatus using the power amplifier circuit.
The 1st invention of the present invention is a power amplifier circuit, comprising:
a first matching circuit which impedance-matches incoming input signals before outputting them;
a first bias circuit connected to an output of said first matching circuit;
a transistor connected to the output of said first matching circuit;
a second bias circuit one end of which is connected to the output of said transistor;
a second matching circuit which is connected to the output of said transistor and impedance-matches output signals of said transistor before outputting them;
voltage transformation means whose output is connected to the other end of said second bias circuit and whose input is connected with a power supply; and
control means of controlling operation of said voltage transformation means,
wherein said power amplifier circuit further comprises load impedance detecting means of detecting the load impedance on the output side of said power amplifier circuit,
said control means changes output voltage of said voltage transformation means based at least on the results of said detection by said load impedance detecting means, and
said output voltage is applied to said transistor as a supply voltage.
The 2nd invention of the present invention is the power amplifier circuit according to 1st invention, further comprising an isolator disposed between said load impedance detecting means and an antenna.
The 3rd invention of the present invention is the power amplifier circuit according to 1st or 2nd inventions, wherein said load impedance detecting means comprises:
(1) a directional coupler which outputs a signal from one terminal according to received signal outputted from said second matching circuit to a load side and outputs a signal from the other terminal according to reflected waves inputted from said load side;
(2) a first detector which outputs data on the amplitude and phase of a signal outputted from said one terminal; and
(3) a second detector which outputs data on the amplitude and phase of a signal outputted from said other terminal.
The 4th invention of the present invention is the power amplifier circuit according to any one of 1st to 3rd inventions, wherein said control means controls the value of said supply voltage of said transistor according to the value of load impedance, which is the results of said detection by said load impedance detecting means.
The 5th invention of the present invention is the power amplifier circuit according to 4th invention, wherein said control means comprises storage means of storing, as a table, data which represents correspondence between the value of said load impedance and the value of said supply voltage and which is used for said control.
The 6th invention of the present invention is a power amplifier circuit, comprising:
a first matching circuit which impedance-matches incoming input signals before outputting them;
a first bias circuit connected to an output of said first matching circuit;
a transistor connected to the output of said first matching circuit;
a second bias circuit one end of which is connected to the output of said transistor;
a second matching circuit which is connected to the output of said transistor and impedance-matches output signals of said transistor before outputting them;
voltage transformation means whose output is connected to the other end of said second bias circuit and whose input is connected with a power supply; and
control means of controlling operation of said voltage transformation means,
wherein said voltage transformation means delivers output voltage under the control of said control means, and
said control means determines according to output power from said power amplifier circuit whether to make said voltage transformation means carry out a step-up operation of raising said output voltage above a preset supply voltage or a step-down operation of lowering said output voltage below said supply voltage.
The 7th invention of the present invention is the power amplifier circuit according to 1st invention, wherein said control means controls the value of said supply voltage of said transistor according to the value of load impedance, which is the results of said detection by said load impedance detecting means, as well as to the value of output power of said power amplifier circuit.
The 8th invention of the present invention is the power amplifier circuit according to 7th invention, wherein said control means comprises storage means of storing, as a table in accordance with said output power, data which represents correspondence between the value of said load impedance and the value of said supply voltage and which is used for said control.
The 9th invention of the present invention is the power amplifier circuit according to 1st or 6th inventions, wherein said voltage transformation means is a DC/DC converter.
The 10th invention of the present invention is the power amplifier circuit according to 9th invention, wherein said DC/DC converter is of a step-up/step-down type.
The 11th invention of the present invention is a control method for a power amplifier circuit which comprises:
(1) a first matching circuit which impedance-matches incoming input signals before outputting them;
(2) a first bias circuit connected to an output of said first matching circuit;
(3) a transistor connected to the output of said first matching circuit;
(4) a second bias circuit one end of which is connected to an output of said transistor;
(5) a second matching circuit which is connected to the output of said transistor and impedance-matches output signals of said transistor before outputting them;
(6) voltage transformation means whose output is connected to the other end of said second bias circuit and whose input is connected with a power supply; and
(7) control means of controlling operation of said voltage transformation means,
wherein load impedance on the output side of said power amplifier circuit is detected,
said control means changes output voltage of said voltage transformation means based at least on said detected load impedance, and
said output voltage is applied to said transistor as a supply voltage.
The 12th invention of the present invention is a portable terminal apparatus comprising:
an antenna used for transmission and reception;
transmitting circuit means including the power amplifier circuit according to 1st or 6th inventions for outputting transmission signals from said antenna;
receiving circuit means for processing received signals from said antenna; and
transmission/reception separator circuit means installed between said antenna and said transmitting circuit means and said receiving circuit means.